The present invention relates to a process for glossing a developer sheet and an apparatus useful therein.
The developer sheet of the present invention can be used in conjunction with conventional pressure-sensitive copy paper or photosensitive imaging systems employing microcapsules to provide visible images upon contact with a color precursor which is image-wise released from the microcapsules and transferred to the developing sheet.
Photosensitive imaging systems employing microencapsulated radiation sensitive compositions are the subject of commonly assigned U.S. Pat. Nos. 4,399,209 and 4,416,966 as well as copending U.S. patent application Ser. No. 320,643, filed Jan. 18, 1982. These imaging systems are characterized in that an imaging sheet including a layer of microcapsules containing a photosensitive composition in the internal phase is image-wise exposed to actinic radiation. In the most typical embodiments, the photosensitive composition is a photopolymerizable composition including a polyethylenically unsaturated compound and a photoinitiator and is encapsulated with a color precursor. Exposure image-wise hardens the internal phase of the microcapsules.
U.S. Pat. No. 4,399,209 discloses a transfer system in which the imaging sheet is assembled with a developer sheet prior to being subjected to a rupturing force. Upon passing through the pressure rollers in contact with the developer sheet, the microcapsules rupture and image-wise release the internal phase whereupon the color precursor migrates to the developer sheet where it reacts with a dry developer and forms a color image. The imaging system can be designed to reproduce monochromatic or polychromatic full color images.
Processes for glossing a developer sheet are known in the art. In most cases, heat is used to provide a glossy finish while in some situations, heat and pressure are used. For example, see commonly assigned U.S. Pat. No. 4,554,235. Typically, the developer sheet is glossed by heating in contact with a heated roller or a pair of heated rollers. Also, the developer sheet can be passed over a heated platen. Alternatively, the developer sheet can be placed in a hot oven.
Heated convex surfaces are useful for imparting heat to sheet material. For example, in U.S. Pat. No. 1,399,160, a heated convex surface imparts heat to a paper to which wax is subsequently applied. U.S. Pat. No. 1,913,704 teaches that a heated convex surface imparts heat to a used carbon paper so that the paper coating softens and flows to fill the bare spots on the paper.
A heated convex surface is also used in U.S. Pat. No. 3,621,201 for heat developing paper. The reference teaches the use of a previously exposed heat-sensitive paper such as a non-thermoplastic silver emulsion paper. The paper is fed between the heated convex surface and an endless cloth belt which is held snugly against the convex surface. The belt is driven so as to move the paper over the convex surface. Means are provided for heating the convex surface and controlling the temperature thereof.
Known processes for glossing developer sheets suffer from numerous disadvantages when applied to the present developer sheet. Thermoplastic developer resins, which are capable of forming a film upon the application of heat, are extremely sticky compared to dry silver film, conventional film and xerographic copies; thus, the release conditions of the developer sheet surface are more critical. In hot roller glossing methods, the high contact pressure causes adhesion of the thermoplastic developer resin to the hot rollers. In methods involving heated surfaces, adhesion of the thermoplastic developer resin is also a problem. In addition, an excessive heat transfer rate from the heated surface can ruin the flatness of the sheet. Also, known glossing methods do not achieve an even gloss with respect to image density and are also slow. Additionally, the energy requirements of glossing processes are higher than known photographic, glossing and xerographic toner fusing technologies.
Thus, a need exists in the art for a process for glossing developer sheets and an apparatus useful therein wherein no adhesion of the thermoplastic developer resin to another surface results, sheet flatness is maintained, a more even gloss with respect to image density is achieved and a high throughput is achieved.